Graeme McDowell reached the third round of the World Golf Championships-Accenture Match Play Championship for the first time with a 4 and 2 victory over Ryder Cup team-mate Ross Fisher.
But his fellow Ulsterman Rory McIlroy was on the receiving end of a heavy loss in Tucson.
The 21 year old, who could have ended this week as the World Number Three and ahead of Tiger Woods for the first time in his life, was beaten eight and seven by American Ben Crane.
There has only ever been one bigger margin in the 12-year history of the event. That was when Woods beat Canadian Stephen Ames 9 and 8 five years ago.
McIlroy fell behind instantly by bogeying the first and was then left helpless as Crane, currently ranked 38th in the world, breezed to the turn in an approximate five under par 31.
That was good enough for a six-hole lead, McIlroy then started the back nine as he began the match and after finding more trouble on the next he conceded without ever reaching the green.
In the first of two clashes between members of Europe's Ryder Cup side last October McDowell lost the first to Fisher, but was soon in control.
The Englishman was a semi-finalist two years ago and also won golf's other World Match Play event that season, but after coming back from two down to level by the seventh he immediately lost the next two.
Twice Fisher cut the gap to one, but he conceded the 14th and McDowell chipped to five feet for a winning birdie on the next.
Paul Casey's hopes of a third successive final were hanging by a thread when he trailed Australian Jason Day by three with five to play.
Casey, having squeezed through at the first extra hole in another Ashes duel with Richard Green on the opening day, bogeyed the fourth and seventh and was unable to make a real impression on his opponent around the turn.
In the other European Ryder Cup duel Luke Donald was one up on Edoardo Molinari with six to go, while in the one game featuring two of Corey Pavin's side at Celtic Manor fourth seed Phil Mickelson turned three down to rising star Rickie Fowler.
Ian Poulter's conqueror Stewart Cink was beaten 4 and 3 by Korean Y E Yang, while Thomas Björn, having put out Woods at the 19th in one of the stand-out performances of the opening day, was level with twice winner Geoff Ogilvy after eight.
World Number One Lee Westwood, who has never made it to Friday in ten previous attempts, was two down after six to American Nick Watney - the player who beat him last year - and Justin Rose was level with second seed Martin Kaymer after four.
Crane said: "That was one of the best rounds I've ever played in my life. Rory had a couple of balls in the desert, but I played exceptional and the round went all my way."
McDowell, a stablemate of Fisher, stated: "It's always funny against a friend. It's difficult to get the killer instinct, that edge that you need.
"We threw each other a few holes, but thankfully I was able to hang in there and get the job done. It wasn't pretty, but sometimes you can win ugly."
He next plays Yang, who beat Woods head-to-head for his first Major title two years ago.
There was no way back for Casey. He did stay alive by winning the driveable 15th, but Day hit his tee shot to within six feet on the next and did not even have to putt.
Day, ranked 40th in the world, said: "I was just very happy with how I handled myself. Paul's a very strong match play player."
It looked as though Casey would not be the highest seed beaten in the round, though.
Mickelson fell two down to Fowler after 11 and Westwood was two down to Watney before taking the eighth.
Fowler sent Mickelson to easily his biggest defeat in the tournament, and did it in real style with eagles on the 11th and 13th for a stunning 6 and 5 victory.
It was a result that means Europe are certain to have the world's top three at the end of the week and possibly the top four, with McDowell and Donald both having the chance to tuck in behind Westwood and Kaymer.
Donald was two up with three to go on Molinari.
There was yet another upset when Ernie Els horseshoed out of the hole at the last and was beaten by JB Holmes, the American who came into the field on Tuesday for the injured Tim Clark.
And the shocks went on with 17 year old Matteo Manassero following his victory over Steve Stricker with a final green success over Charl Schwartzel.
Manassero was the sole remaining Italian when Donald saw off Molinari at the 17th, while Westwood was two down with six to go and Rose one behind at the turn.
Westwood missed another chance on the 13th, but birdied the next to be only one down again, while Rose was only one behind Kaymer with six to go.
Westwood, having three-putted the 16th for only a half, should have been out on the next, but Watney missed a four footer.
Björn could not follow up his win over Woods with another win, bogeying the last to lose to twice winner Geoff Ogilvy.
Rose, meanwhile, had four birdies in five holes and was level with Kaymer with three to go.
